Dear Fishboat: I agree almost with Jeff.
Where you can hear an improvement is when you change the inductors and capacitors ( less with the resistors, but you can try. ).
The Alphacore inductores are the best that I know, I'm using the silver wire version, better than the cooper one.
About the capacitors: I already try almost every cap out there, including the Sonicaps that are very good, and I think that the best are the ones from V-caps: hands down any other cap in the market for a speaker crossovers.
For the resistors, nothing come close like Mills resistors.
Where I disagree with Jeff is about the variable resistors, because this ones are used to " tame " some internally design parameters and maybe you could use it for align something in the speaker crossover.
Now, if after you change the caps and inductors you think that everything is Ok, then you can follow to change that variable resistors for good fixed ones ( Caddock ).
Regards and enjoy the music.